<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .father {
            height: 500px;
            width: 500px;
            background-color: hotpink;
            /* 1.父亲安置边框 */
            /* border-top: 1px solid transparent; */
            /* 2.父亲给padding 值  */
            /* padding-top: 1px; */
            /* 3.父亲给一个overflow:hidden. */
            overflow: hidden;
        }
        
        .son {
            height: 200px;
            width: 200px;
            margin-top: 50px;
            background-color: skyblue;
        }
    </style>
</head>

<body>
    <div class="father">
        <div class="son"></div>
    </div>
</body>

</html>